Bath and process for producing platinum metal immersion deposits



3,337387 BATH AND PROCESS FUR iPRQDUClNG PLATI- NUM METAL EMMERSEGNDEPUSHS Ronald Wiiiiarn .lohnson, Harrow, Middlesex, England, assigrrorto The international Nickel Company, ind, New York, NFL, a corporationof Delaware No Drawing. Filed Apr. 23, 1965, Ser. No. 451,543 Claimspriority, appiication Great Britain, Apr. 28, 19 .64, 17,579/64 11Claims. (Ci. 117-71) ABSTRACT UP THE DESCLGSURE Directed to a processfor producing an immersion deposit of a metal from the group consistingof palladium, platinum, rhodium and ruthenium upon a metal substratewherein the plating bath contains about 1 to about 10 grams per liter ofone of the aforementioned platinum group metals, about 64 to about 96grams per liter of hydrochloric acid, about 0.1 to about 2.5 grams perliter of copper, and up to about 5 grams per liter of ferrous iron. Theresulting deposits are particularly useful in producing soldcrablecoatings.

The present invention is directed to the immersion plating of platinummetals and, more particularly, to an improved immersion plating bath andprocess for producing immersion deposits of platinum metals upon nickeland nickel alloy substrates.

It is known that coatings consisting wholly or partly of platinum metalscan be formed on metals and alloys by immersion in acid aqueoussolutions of salts of palladium, platinum, rhodium and ruthenium. Copperand copper alloys are readily coated in this way but on other metals itis difficult to obtain consistent results or, in some cases, any coatingat all. These difiiculties are particularly great when the metal oralloy to be coated contains residual deoxidizing elements added duringmelting and they are believed to be due to the formation of oxide layerson the surface. For example, it is dllTlClllt to form adherent coatingson nickel and on nickel-iron alloys and very diiiicult if these alloyscontain traces of calcium, silicon or magnesium, which are oftenincorporated in such alloys as deoxidants.

I have now found that adherent coatings of a metal from the groupconsisting of palladium, platinum, rhodiurn and ruthenium can beproduced by employing a special immersion coating bath.

It is an object of the present invention to provide an improvement inthe production of platinum metal immersion plates upon substrates madeof nickel and of nickel-iron alloys.

It is another object of the invention to provide a special immersionplating bath particularly adapted for the production of coatings made ofplatinum, palladium, rhodiurn and ruthenium on nickel and on nickel-ironalloys.

It is a further advantage of the invention to provide a process wherebyimmersion coatings of palladium, platinum, rhodium and ruthenium can beproduced on nickel and on nickel alloy substrates.

Other objects and advantages of the invention will become apparent from.the following description.

Generally speaking, I have now surprisingly found that the formation ofadherent coatings is facilitated by the presence of cupric or cuprouscopper or ferrous iron in aqueous acid platinum metal immersion coatingsolutions. Iron alone is less effective than copper or copper plus ironand, advantageously, the solutions contain at States Patent c lC leastabout 0.1 or about 0.2 gram per liter (g.p.l.) copper with or withoutiron. Very satisfactory results are obtained with l g.p.l. copper orwith a mixture of 0.5 g.p.l. copper and 0.5 g.p.l. iron and thesolutions preferably contain from 0.5 to 2.5 g.p.l. copper. There is noadvantage in increasing the copper content above 2.5 g.p.l., thoughlarger amounts, e.g., up to 5 g.p.l., may be present if desired. Theiron content preferably does not exceed 2.5 g.p.l. but some improvementin adhesion is obtained at iron contents up to 5 g.p.l.

The metal coatings are formed by chemical replacement of the basis metaland the acidity of the solution must be such that the replacementreaction will proceed to the desired extent. Hence, if more than a verythin coating is required, the acidity must be high enough to insure thatmore of the basis metal is attacked and dissolved than is replaced bythe coating metal so that a porous coating results through which attackon the surface can continue. If the acidity is too low, a nonadherentdeposit will be obtained or a thin, nonporous coating will be formed andthe reaction will then cease, while if the acidity is too high, anadherent coating will not be formed. Advantageously, the free acidcorresponds to the salt of the platinum metal in the solution. Forpalladium, platinum and rhodium, I prefer to use solutions of thechloride in hydrochloric acid while for ruthenium the solutionpreferably consists of ammonium nitroso ruthenium chloride or rutheniumsulfamate in hydrochloric acid.

The concentration of the platinum metal in the solution is suitably from1 to g.p.l. and the concentration of hydrochloric acid from 200 to 300milliliters per liter of concentrated (32% by weight per unit volume)acid, i.e., about 64 to 96 g.p.l. of HCl. My preferred solutions contain5 g.p.l. of platinum metal and 250 milliliters per liter of concentratedhydrochloric acid (80 grams per liter of HCl).

The solutions of the invention are particularly useful for coatingnickel and nickel alloys, e.g., nickel-iron alloys containing up toabout 65% iron and the balance essentially nickel, to produce soldcrablecoatings thereon. Nickeliron alloys, particularly the alloy containing50% nickel and 50% iron, are used as electric conductors for sealingthrough glass in electrical and electronic apparatus, and in switchingapparatus such as reed switches, but have the disadvantage that they arenot easy to solder. It is known that their solderability can be improvedby coating them with palladium or other metals and, according to afurther feature of the present invention, I make use of my solutions tocoat the alloys by immersion. I find, for example, that by the use of mypreferred palladium solution, good adherent coatings are obtained whichcan reliably be tinned by an automatic dipping process.

The comparative results set out in the table below illustrate theadvantages of the present solutions.

Specimens were cut from a strip of 56% nickel-5 0% iron alloy made byair melting and containing residual deoxidants (including magnesium) andwere cleaned by dipplug in acetone and then in a hot detergent solution,rinsing with water, immersion for one minute in concentratedhydrochloric acid at room temperature and again rinsing with water. Theywere then immersed for five minutes in an aqueous solution maintained atC. to C. and containing 5 g.p.l. of palladium (added as sodiumtetrachloropalladate), 250 milliliters per liter of 32% by weight perunit volume hydrochloric acid and the indicated amounts of copper andiron, added as cupric and ferrous chlorides, respectively. The coatedspecimens were immersed in boiling water for 10 minutes to clean thepores of the coating, dried, and then tested for solderability by odipping them in a proprietary flux and then immersing them in puremolten tin at 260 C. for two seconds. The appearance and adhesion of thecoatings and an assessment of their solderability are recorded in thefollowing The invention is useful for the production of plated contacttips in electrical switching and the like and in instances wheredifficulty in soldering of the alloy employed in such applications, forexample, nickel-iron alloys, has

table. 5 been encountered.

Solution Cu, Fe, Adhesion Appearance Solderability No. g.p.l. g.p.l.

0 0 Very poor 0.1 0 Moderate Dull Good when adherent. 0.5 0 Good Shghtlydull Goo 0 0.5 Dull, darkish-.- Good when adherent. 0.5 0.5 Bright Good.1.0 0 .do Do. 0 1.0 Dull, darkish..- Good when adherent. 2.5 0 d Brig tGood. 5. 0 0 do -1 Slightly dulL-.- D0. 0 6.0 Poor Dark Solution No. 6also produced a bright, adherent deposit on commercially pure nickelwhereas Solution No. 1 failed to produce an adherent deposit on anotherspecimen of the nickel. In another test, a solution similar to SolutionNo. 6 containing 1 gram per liter of copper added as cuprous chloride(Cu Cl gave a substantially identical result in the immersion plating ofa 50% nickel-50% iron alloy.

In contrast to the favorable effects of additions of cupric or cuprouscopper and ferrous iron, the addition to Solution No. 1 of cobalt,manganese, ferric iron, chromium or lead, each in an amount of l g.p.l.,brought about no improvement in the coating.

Besides nickel and the aforementioned nickel-iron a1- loys, other metalsand alloys that can be coated include nickel-chromium alloys andnickel-cobalt-chromium alloys, both with and without titanium oraluminum or both. Thus, alloys containing up to about 25% chromium, upto about 25% cobalt, up to about 65% iron, up to about 10% of aluminumand titanium, with the balance essentially nickel, can be coated inaccordance with the invention. Adherent deposits are not formed on mildsteel or 18% chromium-8% nickel stainless steel. Nickel-chromium andnickel-chromium-cobalt alloys on which Solution No. 1 failed to form anadherent deposit, when used as described above, are an alloy containingchromium 20% and titanium 0.4% with the balance nickel and impurities;and an alloy containing chromium 20%, cobalt 18%, titanium 2.4% andaluminum 1.4% with the balance nickel and impurities. On the other hand,Solution No. 6 gave bright adherent coatings on each of these.

To illustrate the application of the invention to solutions of othermeals, specimens of the 50% nickel-50% iron alloy and of commerciallypure nickel similar to those used in the previous tests were immersedfor 5 minutes at 65 C. in an aqueous solution containing 5 g.p.l. ofplatinum and 250 milliliters per liter of concentrated hydrochloricacid. No adherent deposit was formed. Addition of 1 g.p.l. of copper tothe solution resulted in the formation of an adherent, solderabledeposit on the nickel and the nickel-iron alloy. Adherent solderabledeposits were also obtained On specimens of this alloy by the use ofsolutions containing 5 g.p.l. of rhodium and 250 mil liliters per literof concentrated hydrochloric acid (5 minutes immersion at roomtemperature) and solutions containing 5 g.p.l. of ruthenium (added asammonium nitroso ruthenium chloride) and 250 milliliters per liter ofconcentrated hydrochloric acid (5 minutes immersion at 65 C.).

The coatings formed by means of the invention using copper-containingsolutions contain substantial amounts of copper in addition to theplatinum metal. The coatings are quite thin, for example, the coatingsproduced on a 50% iron-50% nickel alloy by immersion for 5 minutes at 20C. to C. using Solution No. 6 were estimated to be about 0.13 micron inthickness. The corrosion resistance of the coatings, which tend to beporous, can be improved by sealing with gold applied by immersionplating or by forming a water insoluble substance in the pores.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

1. The process for producing a solder coating on articles made of nickeland nickel-iron alloys which comprises immersing said article in an acidaqueous immersion plating bath containing about 1 to about 10 grams perliter of platinum, about 64 to about 96 grams per liter of hydrochloricacid, about 0.2 to about 2.5 grams per liter of copper, and up to about5 grams per liter of ferrous iron to form upon the immersed surface ofsaid article an adherent platinum coating, drying the platinumcoatedarticle and immersing the platinum-coated portion thereof in a bath ofmolten tin solder to form upon said platinum-coated portion an adherentcoating of tin solder.

2. The process for producing a solder coating on articles made of nickeland nickel-iron alloys which comprises immersing said article in an acidaqueous immersion plating bath containing about 1 to about 10 grams perliter of palladium, about 64 to about 96 grams per liter of hydrochloricacid, about 0.2 to about 2.5 grams per liter of copper, and up to about5 grams per liter of ferrous iron to form upon the immersed surface ofsaid article an adherent palladium coating, drying the palladium-coatedarticle and immersing the palladium-coated portion thereof in a bath ofmolten tin solder to form upon said palladium-coated portion an adherentcoating of tin solder.

3. The process for producing an immersion plated deposit of a platinummetal upon a metal substrate made of a metal containing up to about 25chromium, up to about 25% cobalt, up to about 65 iron, up to about 10%of metal from the group consisting of aluminum and titanium, with thebalance essentially nickel, which comprises immersing said article in anacid aqueous immersion plating bath containing about 1 to about 10 gramsper liter of a metal from the group consisting of platinum, palladium,rhodium and ruthenium, about 64 to about 96 grams per liter ofhydrochloric acid, about 0.1 to about 2.5 grams per liter of copper andup to about 5 grams per liter of ferrous iron to form upon the immersedsurface of said article an adherent platinum metal coating.

4. The process according to claim 3 wherein the copper content of theimmersion plating bath is about 1 gram per liter.

5. A metal immersion plating bath comprising about 1 to about 10 gramsper liter of a metal from, the group consisting of platinum, palladium,rhodium and ruthenium, about 64 to about 96 grams per liter ofhydrochloric acid, about 0.1 to about 2.5 grams per liter of copper, upto about 5 grams per liter of ferrous iron and the balance essentiallywater.

6. A metal immersion plating bath according to claim 5 wherein the metalis palladium.

7. A metal immersion plating bath according to claim 5 wherein the metalis platinum.

8. A metal immersion plating bath according to claim 5 wherein the metalis rhodium.

9. A metal immersion platingbath according to claim 5 wherein the metalis ruthenium.

10. A metal immersion plating bath according to claim 5 wherein thecopper content is about 0.2 to about 2.5 grams per liter.

11. A metal immersion plating bath according to claim 5 wherein thecopper content is about 1 gram per liter.

References Cited UNITED STATES PATENTS Harris 11713O XR Certa et al11713O XR Robinson 117-130 XR Knapp et a1 1l7130 XR ALFRED L. LEAVITT,Primary Examiner.

10 W. F. CYRON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 3 387987 June 11 1968 Ronald William Johnson It is certified that error apatent and that said Letter shown below:

ppears in the above identified 5 Patent are hereby corrected as In theheading to the printed specification, line 8,

"Apr 28 1964 should read Apr 20 1965 Column 1 line 61 "and" should reador Column 3 l ine 48 "meals" should read metals Signed and sealed thi s28th day of Octobe r l 969 (SEAL) Attest:

Edward M. Fletcher, Jr. kttesting Officer Commissioner of PatentsWILLIAM E. SCHUYLER, JR.

